It has long been recognized that stable suspensions of pulverized coal and a liquid hydrocarbon are desirable mixtures for use as commercial fuels. Numerous attempts have been made to form stable mixtures of crushed coal and crude or refined hydrocarbons. Many attempts have failed because equipment with high energy requirements has been required. Other attempts have failed because water has been required, thus reducing the BTU content of the resultant mixture. Other procedures have failed due to the instability of the resultant mixture.
In an attempt to provide stable mixtures the prior art is replete with attempts to include chemical compounds that will stabilize the mixture so that the coal remains suspended in the liquid hydrocarbon. The degree of success of these stabilizers has varied from ones that are not effective to those that represent a significant improvement in comparison to no stabilizer at all. However, such stabilizers still fail to achieve all desired performance characteristics.
In Japanese Patent Application No. 53-123408 published Oct. 27, 1978, there are disclosed quaternary ammonium salts where the salt radical includes a halogen atom. One commercially available example of such a compound is dicocodimethylammonium chloride having the structure ##STR1## and sold under the trademark Arquad 2C-75 by Armak Industrial Chemical Division of Armak Company, Inc.
Rowell et al U.S. Pat. No. 4,201,552 discloses a tertiary amine or a quaternary ammonium salt that contains the group, N--CH.sub.2 --C--CH.sub.2 --O--. This quaternary ammonium salt is stated to be available under the trademark Atlas G-271. In a subsequent publication by the inventors the compounds of the above Japanese Patent Application are described as being more effective than Atlas G-271.
It has been one objective of this invention to provide an effective coal-oil mixture stabilizer. It has been another objective to provide such a stabilizer that does not significantly increase the viscosity of the coal oil mixture to a point where it is not readily pumpable with conventional equipment. Another important objective has been to provide a stabilizer that significantly increases the length of time the mixture can be stored without significant sedimentation occurring. These and other objectives will become more apparent from the following description.